Biomedical subjects

Stephen A Jesch

Publications and source records attributed to Stephen A Jesch.

6 recordsLinked to original sources

PubMed2006

The emergence of yeast lipidomics.

The emerging field of lipidomics, driven by technological advances in lipid analysis, provides greatly enhanced opportunities to characterize, on a quantitative or semi-quantitative level, the entire spectrum of lipids, or lipidome, in specific cell types. When combined with advances in other high throughput technologies in genomics and proteomics, lipidomics offers the opportunity to analyze the unique roles of specific lipids in complex cellular processes such as signaling and membrane trafficking. The yeast system offers many advantages for such studies, including the relative simplicity of its lipidome as compared to mammalian cells, the relatively high proportion of structural and regulatory genes of lipid metabolism which have been assigned and the excellent tools for molecular genetic analysis that yeast affords. The current state of application of lipidomic approaches in yeast and the advantages and disadvantages of yeast for such studies are discussed in this report.

Gene Expression Regulation, Fungal↗

PubMed2006

Inositol induces a profound alteration in the pattern and rate of synthesis and turnover of membrane lipids in Saccharomyces cerevisiae.

The addition of inositol to actively growing yeast cultures causes a rapid increase in the rate of synthesis of phosphatidylinositol and, simultaneously, triggers changes in the expression of hundreds of genes. We now demonstrate that the addition of inositol to yeast cells growing in the presence of choline leads to a dramatic reprogramming of cellular lipid synthesis and turnover. The response to inositol includes a 5-6-fold increase in cellular phosphatidylinositol content within a period of 30 min. The increase in phosphatidylinositol content appears to be dependent upon fatty acid synthesis. Phosphatidylcholine turnover increased rapidly following inositol addition, a response that requires the participation of Nte1p, an endoplasmic reticulum-localized phospholipase B. Mass spectrometry revealed that the acyl species composition of phosphatidylinositol is relatively constant regardless of supplementation with inositol or choline, whereas phosphatidylcholine acyl species composition is influenced by both inositol and choline. In medium containing inositol, but lacking choline, high levels of dimyristoylphosphatidylcholine were detected. Within 60 min following the addition of inositol, dimyristoylphosphatidylcholine levels had decreased from approximately 40% of total phosphatidylcholine to a basal level of less than 5%. nte1Delta cells grown in the absence of inositol and in the presence of choline exhibited lower levels of dimyristoylphosphatidylcholine than wild type cells grown under these same conditions, but these levels remained largely constant after the addition of inositol. These results are discussed in relationship to transcriptional regulation known to be linked to lipid metabolism in yeast.

Cell Membrane↗

PubMed2006

Multiple endoplasmic reticulum-to-nucleus signaling pathways coordinate phospholipid metabolism with gene expression by distinct mechanisms.

In many organisms the coordinated synthesis of membrane lipids is controlled by feedback systems that regulate the transcription of target genes. However, a complete description of the transcriptional changes that accompany the remodeling of membrane phospholipids has not been reported. To identify metabolic signaling networks that coordinate phospholipid metabolism with gene expression, we profiled the sequential and temporal changes in genome-wide expression that accompany alterations in phospholipid metabolism induced by inositol supplementation in yeast. This analysis identified six distinct expression responses, which included phospholipid biosynthetic genes regulated by Opi1p, endoplasmic reticulum (ER) luminal protein folding chaperone and oxidoreductase genes regulated by the unfolded protein response pathway, lipid-remodeling genes regulated by Mga2p, as well as genes involved in ribosome biogenesis, cytosolic stress response, and purine and amino acid metabolism. We also report that the unfolded protein response pathway is rapidly inactivated by inositol supplementation and demonstrate that the response of the unfolded protein response pathway to inositol is separable from the response mediated by Opi1p. These data indicate that altering phospholipid metabolism produces signals that are relayed through numerous distinct ER-to-nucleus signaling pathways and, thereby, produce an integrated transcriptional response. We propose that these signals are generated in the ER by increased flux through the pathway of phosphatidylinositol synthesis.

Amino Acids↗

PubMed2004

Genome-wide analysis reveals inositol, not choline, as the major effector of Ino2p-Ino4p and unfolded protein response target gene expression in yeast.

In the yeast Saccharomyces cerevisiae, the transcription of many genes encoding enzymes of phospholipid biosynthesis are repressed in cells grown in the presence of the phospholipid precursors inositol and choline. A genome-wide approach using cDNA microarray technology was used to profile the changes in the expression of all genes in yeast that respond to the exogenous presence of inositol and choline. We report that the global response to inositol is completely distinct from the effect of choline. Whereas the effect of inositol on gene expression was primarily repressing, the effect of choline on gene expression was activating. Moreover, the combination of inositol and choline increased the number of repressed genes compared with inositol alone and enhanced the repression levels of a subset of genes that responded to inositol. In all, 110 genes were repressed in the presence of inositol and choline. Two distinct sets of genes exhibited differential expression in response to inositol or the combination of inositol and choline in wild-type cells. One set of genes contained the UASINO sequence and were bound by Ino2p and Ino4p. Many of these genes were also negatively regulated by OPI1, suggesting a common regulatory mechanism for Ino2p, Ino4p, and Opi1p. Another nonoverlapping set of genes was coregulated by the unfolded protein response pathway, an ER-localized stress response pathway, but was not dependent on OPI1 and did not show further repression when choline was present together with inositol. These results suggest that inositol is the major effector of target gene expression, whereas choline plays a minor role.

Basic Helix-Loop-Helix Proteins↗

PubMed2004

Role of the unfolded protein response pathway in secretory stress and regulation of INO1 expression in Saccharomyces cerevisiae.

The unfolded protein response pathway (UPR) enables the cell to cope with the buildup of unfolded proteins in the endoplasmic reticulum (ER). UPR loss-of-function mutants, hac1Delta and ire1Delta, are also inositol auxotrophs, a phenotype associated with defects in expression of INO1, the most highly regulated of a set of genes encoding enzymes of phospholipid metabolism. We now demonstrate that the UPR plays a functional role in membrane trafficking under conditions of secretory stress in yeast. Mutations conferring a wide range of membrane trafficking defects exhibited negative genetic interaction when combined with ire1Delta and hac1Delta. At semipermissive temperatures, carboxypeptidase Y transit time to the vacuole was slower in Sec(-) cells containing an ire1Delta or hac1Delta mutation than in Sec(-) cells with an intact UPR. The UPR was induced in Sec(-) cells defective in subcellular membrane trafficking events ranging from ER vesicle trafficking to distal secretion and in erg6Delta cells challenged with brefeldin A. However, the high levels of UPR induction observed under these conditions were not correlated with elevated INO1 expression. Indeed, many of the Sec(-) mutants that had elevated UPR expression at semipermissive growth temperatures failed to achieve wild-type levels of INO1 expression under these same conditions.

Basic-Leucine Zipper Transcription Factors↗

PubMed2002

Inheriting a structural scaffold for Golgi biosynthesis.

In animal cells, the Golgi complex undergoes reversible disassembly during mitosis. The disassembly/reassembly process has been intensively studied in order to understand the mechanisms that govern organelle assembly and inheritance during cell division. A long-standing controversy in the field has been whether formation of Golgi structure is template-mediated or self-organizes from components of the endoplasmic reticulum. A recent study1 however, has demonstrated that a subset of proteins that form a putative Golgi matrix can be inherited during cell division in the absence of membrane input from the endoplasmic reticulum. The outcome of this study suggests that a templating mechanism for the formation of Golgi structure may exist. This study has important implications for understanding mechanisms that govern Golgi biogenesis.

Animals↗